31 research outputs found

    Assessing the quality of biogeochemical coastal data: a step-wise procedure

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    Coastal areas host valuable but vulnerable marine ecosystems subjected to increasing anthropogenic pressure and climate change consequences. To assess the impact of these pressures, monitoring programs have proliferated in coastal areas, but most of them follow locally established procedures for quality control (QC). The well-established QC procedure of open ocean data cannot simply be extended to the highly variable coastal area, for which there is the need to develop ad hoc QC approaches. This is particularly crucial for long-term time series, where different instrumentation and analytical methods have been applied over time. This study, based on the biogeochemical dataset collected over 30 years at the LTER MareChiara station (LTER-MC, Gulf of Naples, Mediterranean Sea), addresses potential discrepancies in a long-term dataset, identifying criteria and methods that could also be applied to other coastal datasets. We developed a serial step-wise procedure to characterize the quality of ~ 84,000 data-points, merging statistical tests and expert knowledge. The procedure included nine tests, each addressing potential problems in data generation and management, some of which of general application and others tailored to specific subsets of data. Based on these test, quality flags were assigned to individual data. Critical tests applied to two other independent datasets, showed that the procedure is not dataset dependent. These results contribute to bridge the gap between the need of objective QC criteria and the intrinsic noise of coastal datasets, promoting the discussion on this topic, and improving a proper management and sharing of coastal data

    Phenological changes of oceanic phytoplankton in the 1980s and 2000s as revealed by remotely sensed ocean-color observations

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    We investigated the phenology of oceanic phytoplankton at large scales over two 5-year time periods: 1979–1983 and 1998–2002. Two ocean-color satellite data archives (Coastal Zone Color Scanner (CZCS) and Sea-viewing Wide Field-of-view Sensor (SeaWiFS)) were used to investigate changes in seasonal patterns of concentration-normalized chlorophyll. The geographic coverage was constrained by the CZCS data distribution. It was best for the Northern Hemisphere and also encompassed large areas of the Indian, South Pacific, and Equatorial Atlantic regions. For each 2° pixel, monthly climatologies were developed for satellite-derived chlorophyll, and the resulting seasonal cycles were statistically grouped using cluster analysis. Five distinct groups of mean seasonal cycles were identified for each half-decade period. Four types were common to both time periods and correspond to previously identified phytoplankton regimes: Bloom, Tropical, Subtropical North, and Subtropical South. Two other mean seasonal cycles, one in each of the two compared 5-year periods, were related to transitional or intermediate states (Transitional Tropical and Transitional Bloom). Five mean seasonal cycles (Bloom, Tropical, Subtropical North, and Subtropical South, Transitional Bloom) were further confirmed when the whole SeaWiFS data set (1998–2010) was analyzed. For ~35% of the pixels analyzed, characteristic seasonal cycles of the 1979–1983 years differed little from those of the 1998–2002 period. For ~65% of the pixels, however, phytoplankton seasonality patterns changed markedly, especially in the Northern Hemisphere. Subtropical regions of the North Pacific and Atlantic experienced a widespread expansion of the Transitional Bloom regime, which appeared further enhanced in the climatology based on the full SeaWiFS record (1998–2010), and, as showed by a more detailed analysis, is associated to La Niña years. This spatial pattern of Transitional Bloom regime reflects a general smoothing of seasonality at macroscale, coming into an apparent greater temporal synchrony of the Northern Hemisphere. The Transitional Bloom regime is also the result of a higher variability, both in space and time. The observed change in phytoplankton dynamics may be related not only to biological interactions but also to large-scale changes in the coupled atmosphere–ocean system. Some connections are indeed found with climate indices. Changes were observed among years belonging to opposite phases of ENSO, though discernible from the change among the two periods and within the SeaWiFS era (1998–2010). These linkages are considered preliminary at present and are worthy of further investigation

    Community-Level Responses to Iron Availability in Open Ocean Plankton Ecosystems

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    Predicting responses of plankton to variations in essential nutrients is hampered by limited in situ measurements, a poor understanding of community composition, and the lack of reference gene catalogs for key taxa. Iron is a key driver of plankton dynamics and, therefore, of global biogeochemical cycles and climate. To assess the impact of iron availability on plankton communities, we explored the comprehensive bio-oceanographic and bio-omics data sets from Tara Oceans in the context of the iron products from two state-of-the-art global scale biogeochemical models. We obtained novel information about adaptation and acclimation toward iron in a range of phytoplankton, including picocyanobacteria and diatoms, and identified whole subcommunities covarying with iron. Many of the observed global patterns were recapitulated in the Marquesas archipelago, where frequent plankton blooms are believed to be caused by natural iron fertilization, although they are not captured in large-scale biogeochemical models. This work provides a proof of concept that integrative analyses, spanning from genes to ecosystems and viruses to zooplankton, can disentangle the complexity of plankton communities and can lead to more accurate formulations of resource bioavailability in biogeochemical models, thus improving our understanding of plankton resilience in a changing environment

    Light sensing and responses in marine microalgae.

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    International audienceMarine eukaryotic phytoplankton are major contributors to global primary production. To adapt and thrive in the oceans, phytoplankton relies on a variety of light-regulated responses and light-acclimation capacities probably driven by sophisticated photoregulatory mechanisms. A plethora of photoreceptor-like sequences from marine microalgae have been identified in omics approaches. Initial studies have revealed that some algal photoreceptors are similar to those known in plants. In addition, new variants with different spectral tuning and algal-specific light sensors have also been found, changing current views and perspectives on how photoreceptor structure and function have diversified in phototrophs experiencing different environmental conditions

    Backward reconstruction of plankton sources in the Gulf of Naples

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    The Gulf of Naples (GoN) is a coastal area of the Southern Tyrrhenian Sea representing a very complex system, influenced by numerous interacting factors depending on the peculiar physical and biogeochemical conditions of this area. Since 2004 a system of HF coastal radars (Sea Sonde CODAR) operates in the GoN providing real time (hourly data) surface current fields with a resolution of 1.0 × 1.0 Km over almost the entire area of the GoN. Moreover plankton abundance in the GoN is monitored weekly at the Long-Term Ecological Research station MareChiara (LTER-MC) since 1984. An oscillating population dynamics, with an alternation, especially in summer, between phases reflecting the coastal and offshore influence on the biological community, has been frequently observed at LTER-MC station. Such an opportunity to integrate biological data and current measurements at high spatio - temporal resolution, makes the GoN a natural laboratory to investigate the role of surface circulation in structuring the marine plankton community. The results here presented refer to a year-long analysis carried out for 2009, which was characterized by a very accurate estimate of the surface dynamics, with a reduced number of HF radar data gaps. A Lagrangian particle transport model, forced by the HF radar current fields, has been applied to identify probable sources and transport pathways of plankton at LTER-MC station. In particular a backward-trajectory modeling approach has been used to reconstruct a probability distribution function around the LTER-MC station. The results from the backward trajectory simulations allowed to identify origin of plankton observed at LTER-MC; the surface dynamics analysis accounted for the relationship between the inter-annual alternation in the plankton community and the variability in the wind-driven circulation

    Exploring the molecular basis of responses to light in marine diatoms

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    International audienceLight is an essential source of energy for life on Earth and is one of the most important signals that organisms use to obtain information from the surrounding environment, on land and in the oceans. Prominent marine microalgae, such as diatoms, display a suite of sophisticated responses (physiological, biochemical, and behavioural) to optimize their photosynthesis and growth under changing light conditions. However, the molecular mechanisms controlling diatom responses to light are still largely unknown. Recent progress in marine diatom genomics and genetics, combined with well-established (eco) physiological and biophysical approaches, now offers novel opportunities to address these issues. This review provides a description of the molecular components identified in diatom genomes that are involved in light perception and acclimation mechanisms. How the initial functional characterizations of specific light regulators provide the basis to investigate the conservation or diversification of light-mediated processes in diatoms is also discussed. Hypotheses on the role of the identified factors in determining the growth, distribution, and adaptation of diatoms in different marine environments are reported
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